System and apparatus for flowing wells



Nov. 29, 1955 R. C. PRYQR SYSTEM AND APPARATUS FOR FLOWING WELLS 5Sheets-Sheet l Filed Feb. ll 1951 6 I w QW F/G 2 INVENToR.

R. c. PRYoR A 7l TORNE Y Nov. 29, 1955 R. c. PRYOR SYSTEM AND APPARATUSvFOR FLOWING WELLS 5 Sheets-Sheet 2 Filed Feb. l, 1951.

INVENTOR. R. C. PRYOR A TTORNEYS Nov. 29, 1955 R. c. PRYOR SYSTEM ANDAPPARATUS FOR FLOWING WELLS 5 Sheets-Sheet 3 -Filed Feb. l, 1951INVENTOR. R. C. PRYOR F/G. 4A

A TTOPNEYS Nov. 29, 1955 R. c. PRYOR SYSTEM AND APPARATUS FOR FLOWINGWELLS 5 Sheets-Sheet 4 Filed Feb. l. 1951 "III,"

Nov. 29, 1955 Filed Feb. l 1951 R. C. PRYOR SYSTEM AND APPARATUS FORFLOWING WELLS 5 Sheets-Sheet 5 INVENTOR. R. c. PRYOR *WMM A TTORNE VSUnited States Patent O 2,725,014 SYSTEM AND APPARATUS FOR FLOWING WELLSRobert C. Pryor, Keytesville, Mo., assignor to Phillips PetroleumCompany, a corporation of Delaware Application February 1, 1951, SerialNo. 208,946 7 Claims. (Cl. 10S- 233) This invention relates to a systemand apparatus for flowing wells. In one embodiment this inventionrelates to a system for flowing Wells wherein fluid controlled valvesare utilized to regulate the addition of lifting gas to productionlluid. In another embodiment this invention relates to a system forowing wells by gas wherein a plurality of uid controlled valves,operating at different controlling fluid pressures and actuated from asingle source at the surface of the well, regulate the addition oflifting gas to production fluid.

In producing wells, it is often necessary to produce large volumes ofwater along with the oil recovered from the well. In such wells, theproduction lluid usually contains large quantities of suspended sand. Itcan readily be seen that to produce the large quantity of productionfluid with sucker rod pumps, the pumps must be actuated very rapidly.This rapid movement, and the suspended sand acting as an abrasive,increases wear on the moving parts of the pump to such an extent that,in many cases, it is uneconomical to produce the Well with a sucker rodpump. When this diiculty is encountered in producing a well, resort isusually made to producing the well by a gas lift system. f

It has been found that the amount of lifting gas necessary to ow a wellat the desired production rate varies over a wide range from well towell and even in the same well over a period of time. For economicreasons it is highly desirable to supply only that amount of lifting gasnecessary to give the desired production. Although much time and efforthas been expended in attempting to calculate the amount of lifting gasnecessary in each case before owing operations are; begun, nosatisfactory method has yet been discovered. Even if such a method werediscovered the problem of furnishing only that amount of lifting gasnecessary to give the desired production at any particular time wouldnot be solved because, as was pointed out above, the amount of liftinggas necessary may vary over a wide range in the same well over a periodof time. Therefore it is highly desirable to have a means of regulatingthe amount of lifting gas supplied to a well at any given time duringthe well flowing operation so as to utilize only that amount of liftinggas necessary to give the desired production.

ln the past, in continuous gas lift systems utilizing spring or iiuidloaded valves, the operation of the valves has been dependent upon apressure differential between the casing and the tubing in the well, orupon the pressure differential between the casing or tubing and a fluidor spring loaded valve, the pressure of the fluid or the tension of thespring of which cannot be varied from the surface of the well. Valves ofthe type mentioned are set to operate at a given pressure differentialbefore being lowered into a well and such a differential cannot bechanged from the surface of the well.

As was pointed out above, the amount of lifting gas necessary to flow awell cannot be calculated before flowing operations are begun and evenif this were possible, the amount of lifting gas necessary in a well mayvary greatly over a period of time. Thus since the fluid or springloaded valves used in the past in continuous well flowing operationsmust be preset to a single pressure differential and since the amount oflifting gas necessary may vary over a wide range, it is apparent thatarranged'sequence.

"ice

4flowing system pulled and the valve settings changed, or

excess lifting gas must be supplied with resulting waste and highlifting costs as the operating pressure of the valves cannot be changedfrom the surface of the well.

By the practice of my invention, the above noted difculties areeliminated. According to my invention, the operation of uid controlledvalves in a continuous well owing system is not dependent upon apressure differential between the well casing and tubing nor upon apreset pressure differential between a fluid loaded valve and the casingortubing.

In my invention, uid controlled .valves are utilized in a continuouswell flowing system and the valves are controlled from a single sourceat the surface of the well thereby permitting a variation in the amountof lifting gas supplied to the well necessary to give desired productionas conditions in a well change. Thus my invention eliminates thenecessity of pulling the gas lift system from the well to reset thevalves when conditions change, and yet realizes the'most economic wellflowing conditions at any given time.

In a continuous gas lift system, it is often desirable to have aplurality of valves vertically spaced in the well and operating atdifferent pressures. By my inven tion, a plurality of lluid controlledvalves, operating at different fluid. pressures, are vertically spacedin a well and controlled through a common source of control fluid from apoint at the surface of the well thereby actuating the valvesindividually from a single control point at the surface of the well.

An object of my invention is to provide a continuous gas lift system forflowing wells wherein fluid controlled valves are utilized and arecontrolled from the surface of the well.

Another object of my invention is to provide a continuous gas liftvsystem for ilowing well wherein fluid controlled valves, operating atdifferent pressures and controlled from the surface of the well, areutilized.

Another object of my invention is to provide a continuous gas liftsystem for flowing wells wherein a plurality' of uid controlled valves,vertically spaced in a well, actuated at dilferent pressures by iluidfurnished through a common source, and controlled from a point l*at thesurface of the well, are utilized.

-rality of uid controlled valves are actuated individually through acommon source of controlling fluid and are controlled from'the surfaceof the well.

Another object of my invention is to provide a continuous gas liftsystem wherein iluid controlled valves are utilized that can be actuatedfrom the surface of the well so that the amount of lifting gas furnishedto said well to obtain desired production may be varied without pullingsaid gas lift system from said well in order to reset said valves.

Another object of my invention is to provide an irnproved iluidcontrolled gas lift valve which can be actuated from the surface of awell in a continuous gas lift system.

Another object of my invention is to provide an improved uid controlledgas lift valve which is adapted to be connected with similar valveswhich are actuatedl at different fluid pressures so as to provide aplurality of such valves vertically spaced in a well so that all thevalves can be individually actuated from the surface of the well througha common source of controlling uid in any pre- Other objects will beapparent to one skilled in the art upon reading the discussion andexamining the drawings herein set forth.

In one embodiment of my invention for owing wells, a plurality of uidcontrolled valves forl regulating the amount of lifting gas suppliedtothe production fluid of a well are vertically spaced on the tubing insaid well. Said valves are actuated. at different pressures through acornmon source of controlling fluid connecting said valves with a pointat the surface of the well.v By varying the pressure of said controllingfluid, said valves may be actuated individually in any preselectedsequence, thereby providing the desired amount of lifting gas at anygiven time in the well in spite of changing conditions in the well. Thusby the practice of my invention, the amount of lifting gas necessary toprovide the desired production rate without Wasting lifting gas isobtained in a continuous well flowing system. By surface control of theiiuid controlled valves utilized in said system, the necessity ofpulling the gas lift system and resetting the valves therein because ofchanges in lifting gas requirements of said well iseliminated.

My invention can be more clearly understood by referring to theaccompanying drawings wherein:

Figure l is a sectional elevationy of. a well to which one embodiment ofmy invention has been applied.

Figure 2 is a sectional elevation of a well to which another embodimentof my invention has been applied.

Figure 3a is a vertical section of an embodiment of a valve suitable forthe practice of my inventionshowing the valve attached to a Well tubing.

Figure 3b is a vertical section of the valve of Figure 3a taken alongline 3b.

Figure 4a is a vertical section of another embodiment of a valvesuitable for the practice of my inventiony showing the valve attached toa well tubing.

Figure 4b is a vertical section of the valve of Figure 4a taken alongline 4b. l

Figure 5a is a vertical section ofv another embodimen of a valvesuitable for the practice of my invention showing the valve attached toa welltubing.

Figure 5b is a Vertical section of the valve of Figure 5a taken alongline 5b.

Figure 6a is a vertical section of still another embodiment of a valvesuitable for the practice of my invention showing the valve attached toa Well tubing.

Figure 6b is a vertical sectionof the valve of Figure 6a taken alongline 6b.

Referring to Figure l, casing 10 surrounds tubing 11 forming annulus 12with static production fluid level 13 and pumping production fluid level14. Fluid controlled valves 16, 17, 18, and 19, preferably of the typeshown in either Figures 4a, 5a, or 6a, are secured to tubing 11 byclamps or other means not shown and control the flow of gas andproduction fluid between the interior of tubing 11y and annulus 12. Thevalvesare controlled by regulating the controlling fluid pressuresupplied to the valves from source 21 through common control fluidsupply means 22. Lifting gas is introduced into annulus 12 1 throughpipe 15- and production uid is withdrawn from tubing 11 through pipe 20.It is within the scope of my invention to secure the valves on theoutside and/ or inside of tubing 11, and to pump lifting gas down thewellthrough annulus 12 and up the well through tubing 11 or to pump thelifting gas down the well through tubing 11 and up the Well throughannulus 12. y

Referring now to Figure 2, casing lsurrounds-tubing 11 forming annulus12 with static production iiuid level 13 and pumping production fluidlevel 14. Fluid controlled valves 23, 24, 25, and 26, preferably ofthertype illustrated in `Figure 3a, are secured to tubing 11 byY clampsor other means not shown and control the flow ofI lifting gas andproduction fluid between the interior ofl tubing 11 and annulus 12. Thevalves are controlled by regulating the controlling fluid pressuresupplied to. the valves from source 21 through common controlling. fluidsupply means 22, and are vented through common venting means 27. Againit is within the scope of my invention to pump lifting gas down the wellthrough annulus 12 and up the well through tubing 11 or to pump thelifting gas down the well through tubing 1l and up the well throughannulus 12. Also the valves can be secured to the outside and/or insideof tubing 11.

Referring now to Figures 3a and 3b, housing 28 forms chamber 29 withpiston 3i) slidably operating therein. O-rings or other sealing means 31and 32 form a seal be tween piston 3i) and the walls of chamber 29.Housing 28 is provided with a first conduit 33 for supplying controllinguid to the valve and a second conduit 34 for venting chamber 29 betweenO rings 31 and 32, each of the conduits being longitudinally disposed inthe wall of housing 28 and extending the length thereof. Conduit 33communicates with one end of chamber 29 for supplying controlling fluidthereto. One end of housing 28'is provided with a plug 35 and the otherend is provided with a cylindrical valve seat 36. Pack-ing 40 preventsleakage between plug 35 and housing 28, and packing 39 prevents leakagebetween valve seat 36 and housing 28. O ring 38 forms a seal betweenpiston 3i) and valve seat 36 when the valve is in a closed position.Housing 28 is supplied with nipple 37 which connects the interior oftubing 11 and chamber 29. Conduits 33 and 34 are adapted at each end forconnection to similar valves through control fluid supply means 22 andvent 27. The valve is secured to tubing 11 by clamps 41. The position ofpiston 30 is determined by the balance of pressure forces acting on it,i. e., when the pressure of the controlling fluid times the area ofpiston 3i)` exposed to the controlling fluid is greater than the sum ofthe forces due to the pressure of the lifting gas times the area ofpiston 30 exposed to the lifting gas and the pressure in chamber 29between O rings 31 and 32 times the area exposed to it, then piston 30will move to a closed position, conversely, when the pressure of thecontrolling fluid times the area of piston 30 exposed to the controllingfluid is less than the sum of the forces due to the pressure of thelifting gas times the area of piston 30 exposed to the lifting gas andthe pressure in chamber 29 between O rings 31: and 3 2 times the areaexposed to it, then piston 3Q will move to an open position.

Referring now to Figures #in and 4b. The elements and operation of thisembodiment of my valve are the sarnc as described in reference toFigures 3a and 3b except that conduit 34: for Venting that portion ofchamber 29 be tween O rings 31 and 32 has beenv omitted from housing 42.in a valve of this type, the volume of chamber 2*) between O rings 31and 32 when the valve is in an open position, should be large withrespect to the volume swept by the piston when it moves to a closedposition in order to avoid excessive build-up of pressure between the Grings.

Referring now to Figures 5a and 5b. The elements and operation of thisembodiment of my valve are also the same as described in reference toFigures 3a and 3b except that conduit 34 has been omitted and nipple 44has been added to housing Li3 for venting that portion of chamber 29between O rings 31 and 32 into tubing 11.

Referring now to Figures 6a and 6b.` The elements and operation of thisembodiment of my valve are again the same asv described in reference toFigures 3a and 3h except that conduit 34 has been omitted from housing45 and' piston 46 no longer forms a seal with the walls of chamber 29 atthe controlling fluid end of the piston and the piston is biased in anopen position by spring means 47.

In the practice of a specific embodiment of my invention, a plurality offluid controlled valves, say four as shown in Figure 2, preferably ofthe type illustrated in Figures 3a and 3b, is secured to the outside oftubing 11 and connected to a common source of controlling fluid throughtube 22 and a common vent 27 such` that the valves are vertically spacedin the well when the tubingis lowered therein. Each valve controls theflow of lifting gas and production fluid between annulus 12 and theinside of tubing 11. The valves are selected so that the ratio of thearea of the piston exposed to the controlling fluid to the area of thepiston exposed to the lifting gas in each valve decreases from the topto the bottom of the well such that as the pressure of the controllingfluid is increased, valve 23 having the largest ratio referred to abovecloses first, valve 24 having the next largest ratio closes second,valve 25 having the third largest ratio closes third, and valve 26having the smallest ratio closes last. Therefore, by the practice of myinvention, it is possible to control a plurality of fluid controlledvalves in a pre-selected sequence from a common source of control fiuid.It is apparent that the valves can be positioned along tubing 11 so asto close in any pre-selected sequence.

As the pressure of the lifting gas supplied to annulus 12 through pipe15 is increased, production fluid is forced down annulus 12, through thevalves, up tubing 11, and is discharged through pipe 20. When staticproduction fluid level 13 falls below valve 23, the pressure of thecontrolling fluid supplied to the valves through common tube 22 fromsource 21 is increased so as to close valve 23 but not close valves 24,25, and 26. Production fluid level 13 continues to fall until pumpingproduction fluid level 14 is reached. As the static production fluidlevel is forced down past each of the valves, the pressure of thecontrolling fluid in tube 22 is increased so as to close that valve suchthat valves 23, 24, and 25 are closed in sequence, and when pumpinglevel 14 is reached, the lifting gas for flowing the well is suppliedthrough valve 26 only. It is apparent that the sequence of closing ofthe valves can be chosen so that any of the valves will be either openor closed, as the particular situation demands, when pumping level 14 isreached.

When utilizing the valves illustrated in Figures 4a, 4b, a, 5b, 6a, and6b in the practice of my invention, the operation is similar to thatdescribed above and therefore will not be repeated. Since the fluidcontrolled valves of my invention are not dependent upon the amount ofpressure of the lifting gas or production fluid for operation, thepressure of the lifting gas supplied to the well can be changed toobtain desired production and the valves still operated in thepreselected sequence by changing the pressure of the controlling fluidat the surface of the well. Therefore, by the practice of my invention,desired production can be obtained without waste of lifting gas orwithout pulling the valves from the well in order to reset them asconditions in the well change or as the rate of production is changed.

Since changes in details of construction and arrangement can be made inthe examples used to illustrate my invention without departing from thespirit and scope thereof, l do not desire to be unduly limited by theexamples but desire to be limited only by the claims herein made.

I claim:

l. A fluid operated gas lift valve which comprises an elongatedcylindrical housing having a chamber therein for receiving anddischarging lifting gas and controlling fluid, a first conduitlongitudinally disposed in the wall of said housing and extending thelength of said housing, said first conduit being adapted at each end ofsaid housing forconnection with other gas lift valves so as to form aseries of said valves controllable from a single source, said firstconduit in each valve communicating withy one end of said chambertherein for supplying controlling fluid thereto, said housing in saidvalve having a first opening therein at the other end of said chamberfor passage of said lifting gas between said chamber and the outer faceof said housing, said housing having a second opening therein at a pointintermediate said first opening and said one end of said chamber forpassage of said lifting gas between said chamber and the outer face ofsaid housing, a piston slidably operating inside said chamber inresponse to changes in pressure of said controlling fluid so as to forma seal between said first opening and said second opening and preventpassage of said lifting gas through said valve when said controllingfluid pressure is increased to close said valve, a first 0 ring on thatend of said piston which is exposed to said controlling fluid foreffecting a seal between said piston and the walls of said chamberthereby forming a separate chamber for controlling fluid, a second Oring on said piston intermediate said first O ring and said secondopening in said housing for effecting a second seal between said pistonand the walls of said chamber, and a second conduit longitudinallydisposed in the wall of said housing and communicating with said chamberintermediate said first and said second O rings for venting that portionof said chamber between said O rings, said second conduit being adaptedat each end of said housing for connection to like conduits in similarvalves so as to form a series of valves vented to a single source.

. 2. A fluid operated gas lift valve which comprises an elongatedcylindrical housing having a chamber therein for receiving anddischarging lifting gas and controlling fluid, a conduit longitudinallydisposed in the wall of said housing and extending the length of saidhousing, said conduit being adapted at each end of said housing forconnection with other gas lift valves so as to form a series of saidvalves controllable from a single source, said conduit in said valvecommunicating with one end of said chamber therein for supplyingcontrolling fluid thereto, said housing in said valve having a firstopening therein at the other end of said chamber for passage of saidlifting gas between said chamber and the outer face of said housing,said housing having a second opening therein at a point intermediatesaid first opening and said one end of said chamber for passage of saidlifting gas between said chamber and the outer face of said housing, apiston slidably operating inside said chamber in response to changes inpressure of said controlling fluid so as to form a seal between saidfirst opening and said second opening and preventing passage of saidlifting gas through said valve when said controlling fluid pressure isincreased to close said valve, sealing means disposed around said pistonforming separate chambers so that said piston is actuated by the actionof controlling fluid tending to seat said piston against the action oflifting gas, the first of said separate chamber being exposed to saidcontrolling fluid, and the volume of the second of said separatechambers, when said piston is in the open position, being large withrespect to the volume swept by the piston when the piston moves to aclosed position.

3. A fluid operated gas lift valve which comprises an elongatedcylindrical housing having a chamber therein for receiving anddischarging lifting gas and controlling uid, a conduit longitudinallydisposed in the wall of said housing and extending the length of saidhousing, said conduit being adapted at each end of said housing forconnection with other gas lift valves so as to form a series of saidvalves controllable from a single source, said conduit in said valvecommunicating with one end of said chamber therein for supplyingcontrolling fluid thereto, said housing in said valve having a firstopening therein at the other end of said chamber for passage of saidlifting gas between said chamber and the outer face of said housing,said housing having alsecond opening therein at a point intermediatesaid first opening and said one end of said chamber for passage of saidlifting gas between said chamber and the outer face of said housing, apiston slidably operating inside said chamber in re sponse to changes inpressure of said controlling fluid so as to form a seal between saidfirst opening and said second opening and preventing passage of saidlifting gas through said valve when said controlling fluid pressure isincreased to close said valve, sealing means disposed around said pistonforming separate chambers so that said piston is actuated by the actionof controlling fluid tending to seat said piston against the action oflifting gas, the first of said separate chambers beingV exposed to said`controlling fluid and a conduit in the second of said separate chambersestablishing communication Ibetween said second chamber and the outerface of said housing.

4. A fluid operated gas lift valve which comprises an elongatedcylindrical housing having a chamber therein for receiving anddischarging lifting gas and controlling fluid, a .conduit longitudinallydisposed in the wall of said housing and extending the length of saidhousing, said conduit being adapted at each end of said housing forconnection with other gas lift valves so as to form a series of saidvalves controllable from a single source, said conduit in said valvecommunicating with one end of said chamber therein for supplyingcontrolling fluid thereto, said housing in said valve having a firstopening therein at the other end of said chamber for passage of saidlifting gas between said chamber and the outer face of said housing,said housing having a second opening therein at a point intermediatesaid first opening and said one end of said chamber for passage of saidlifting gas between said chamber and the outer face of said housing, apiston slidably operating inside said chamber in response to changes inpressure of said controlling fluid so as to form a seal between saidfirst opening and said second opening and prevent passage of saidlifting gas through said valve when said controlling fluid pressure isincreased to close said valve, and a resilient means for normallyholding said piston in an open position.

5. A well flow system in cluding a well c asing and tubing, a pluralityof fluid controlled piston operated lifting gas valves vertically spacedon said tubing in said well for regulating flow of a lifting gas betweenthe exterior and interior of said tubing, each valve comprising acylindrical valve housing having an inlet at the bottom and an outlet inthe side thereof, a nipple connecting said outlet to the interior ofsaid tubing thereby establishing communication between the interior ofsaid housing and said tubing, a valve seat disposed in the inlet end ofsaid housing, a piston slideably operating in said housing to seat insaid valve seat to prevent the ow of lifting gas through said valve, asealing member disposed around said piston adjacent its end oppositesaid valve seat thereby forming an upper separate chamber at the pistonend opposite the valve seat, a second sealing means disposed around saidpiston between said sealing member and the valve outlet thereby forminga separate middle chamber, a conduit longitudinally disposed in the wallof said housing extending the length of said housing to permit the flowof a valve controlling uid therethrough from a source at the surface toa succeeding valve and to communicate with said upper chamber forsupplying a valve controlling Huid thereto tending to seat said pistonagainst the force due to lifting gas on the opposite end of said piston,the ratio of the area of the piston exposed to controlling fluid to thearea of the piston exposed to lifting gas in each valve being such thatthe valves can be actuated in a pre-selected sequence, a second conduitlongitudinally disposed in Athe wall of said housingr extending thelength of said housing to communicate with the middle chamber forventing `said charnber and to form with preceding and succeeding valvesa common vent, common means for connecting said first conduits of saidvalves for supplying said controlling fluid for actuating said pistonsin said valves, common means for connecting said second conduits of saidvalves for venting the chambers of said valves, means accessible at thesurface of said well for varying the pressure of said controlling fluidsupplied to said pistons in said valves through said connecting meansand said rst conduits.

6. A gas lift well flowing system comprising a well tubing; a pluralityof fluid controlled piston operated valves secured to and verticallyspaced along said tubing to regulate ow of lifting gas between theexterior and interior of said tubing, each of said valves comprising ahousing having a ow 'passage therethrough which includes a valveseat,means connecting the A'outlet of said ow passage to the interior ofsaid' tubing, said housing having first and second connected pistonchambers therein, said first piston chamber being of largercross-sectional area than said second chamber, said second chamber beingin communication with said ow passage adjacent to said valve seat, apiston positioned for movement through said second chamber, said pistonbeing of substantially the same cross-sectional area as said secondchamber, one end of said piston forming a valve head engageable withsaid valve seat, a piston head secured to the other end of said pistonwithin said first chamber, said piston head being of substantially thesame cross-sectional area as said first chamber, said piston beingpositioned so that said piston (head moves through said first chamberaway from said second chamber when said valve head moves away from saidValve seat, sealing means disposed between said piston and the walls ofsaid second chamber; and a conduit communicating with the first chambersof each of said valves on the sides of said piston head opposite saidrespective second kchambers to supply operating fluid to each of saidvalves, the inlets of each of said flow passages being in communicationwith regions exterior of said housings so that pressures of lifting gasin said regions tend to move said valve heads awayfrom the valve seatsassociated therewith, the pressure of the operating fluid tending tomove said pistons toward said valve seats, the ratio of the areas ofsaid piston heads and said valve heads in each of said valves being sopreselected that said valves are actuated at preselected pressure ratiosbetween said operating liuid and said lifting gas, said valves beingactuated at different pressures of said operating fluid.

7. A fluid operated gas lift valve comprising a housing having a flowpassage therethrough which includes a valve seat, said housing havingfirst and second connected piston chambers therein, said first pistonchamber being of larger cross-sectional area than said second chamber,said second chamber being in communication with said flow passageadjacent said valve seat, a piston positioned for movement through saidsecond chamber, said piston being of substantially the samecross-sectional area as said second chamber, one end of said pistonforming a valve head engageable with said valve seat, a piston headsecured to the other end of said piston within said first chamber, saidpiston head being of substantially the same cross-sectional area as saidfirst chamber, said piston being positioned so that said piston headmoves through said first chamber away from said second chamber when saidvalve head moves away from said valve seat, sealing means disposedbetween said piston and the walls of said second chamber, and a conduitcommunicating with said first chamber 0n the side of said piston headopposite said second chamber to supply operating fluid, the inlet ofsaid flow passage being iu communication with a region exterior of saidhousing so that the pressure in said region tends to move said valvehead away from said valve seat, the pressure of said operating uidtending to move said piston toward said valve seat, the ratio of theareas of said piston head and said valve head being so preselected thatsaid valve is actuated at a preselected pressure ratio between saidcontrolling uid and said pressure exterior of said housing.

References Cited in the file of this patent UNITED STATES PATENTS1,677,781 Joyner July 17, 1928 2,278,532 Crickmer Apr. 7, 1942 2,446,680Walton Aug. 10, 1948

